The use of chlorine-containing refrigerants, such as chlorofluorocarbons (CFC's), hydrochlorofluorocarbons (HCF's) and the like, as refrigerants in air-conditioning and refrigeration systems has become disfavored because of the ozone-depleting properties associated with such compounds. As a result, it has become desirable to retrofit chlorine-containing refrigeration systems by replacing chlorine-containing refrigerants with non-chlorine-containing refrigerant compounds that will not deplete the ozone layer, such as hydrofluorocarbons (HFC's).
In order for any of the replacement materials to be useful in connection with refrigeration compositions, the materials must be compatible with the lubricant utilized in the compressor. Unfortunately, many non-chlorine-containing refrigeration fluids, including HFC's, are relatively insoluble and/or immiscible in the types of lubricants used traditionally with CFC's and HFC's, including, for example, mineral oils, alkylbenzenes or poly(alpha-olefins). In order for a refrigeration fluid-lubricant combination to work efficiently within a compression refrigeration, air-conditioning or heat pump system, the lubricant must be sufficiently soluble in the refrigeration liquid over a wide range of operating temperatures. Such solubility lowers the viscosity of the lubricant and allows it to flow more easily throughout the system. In the absence of such solubility, lubricants tend to become lodged in the coils of the compression refrigeration, air-conditioning or heat pump system evaporator, as well as other parts of the system, and thus reduce the system efficiency.
Polyalkylene glycol, esterified polyalkylene glycol, and polyol ester lubricating oils have been developed as misicible lubricants for HFC refrigeration liquids. Polyalkylene glycol refrigeration lubricants are disclosed by U.S. Pat. Nos. 4,755,316; 4,971,712, and 4,975,212. Polyalkylene glycol esters are disclosed by U.S. Pat. No. 5,008,028. The polyalkylene glycol and polyalkylene glycol ester lubricating oils are disclosed as being misicible in fluoroalkanes containing one or two carbon atoms and no double bonds.
Consequently fluorocarbon-based fluids have found widespread use in industry for refrigeration system applications, including air-conditioning systems and heat pump applications as well, all of which involve compression refrigeration. Compression refrigeration generally involves changing the refrigerant from the liquid to the vapor phase through heat adsorption at a lower pressure and then from the vapor to the liquid phase through heat removal at an elevated pressure.
While the primary purpose of refrigeration is to remove energy at low temperature, the primary purpose of a heat pump is to add energy at higher temperature. Heat pumps are considered reverse cycle systems because for heating, the operation of the condenser is interchanged with that of the refrigeration evaporator.
The art is continually seeking new fluorocarbon and hydrofluorocarbon-based pure fluids that offer alternatives for refrigeration and heat pump applications. Applicants have come to appreciate that fluoro-olefin-based materials (fluoroalkenes) are of particular interest because they have characteristics that make them environmentally safer substitutes for the presently used fluoroalkanes (HFC's), that despite being safe for the ozone layer are suspected of causing global warming.
Applicant has also come to recognize that refrigeration composition substitutes for HFC's in many cases preferably possess certain performance properties to be considered acceptable substitutes, including acceptable refrigeration characteristics, chemical stability, low toxicity, non-flammability, lubricant compatibility and efficiency in use. The latter characteristic is important in many refrigeration systems, air-conditioning systems and heat pump applications, especially when a loss in refrigeration thermodynamic performance or energy efficiency may have secondary environmental impacts through increased fossil fuel usage arising from an increased demand for electrical energy. Furthermore, it would be advantageous for HFC refrigeration composition substitutes to not require major engineering changes to conventional vapor compression technology and lubricant systems currently used with HFC refrigeration liquids.
Flammability is another important property for many applications. That is, it is considered either important or essential in many applications, including particularly in heat transfer applications, to use compositions which are non-flammable. Thus, it is frequently beneficial to use in such compositions compounds which are nonflammable. As used herein, the term “nonflammable” refers to compounds or compositions which are determined to be nonflammable in accordance with ASTM standard E-681, dated 2002, which is incorporated herein by reference. Unfortunately, many HFC's which might otherwise be desirable for used in refrigerant compositions are not nonflammable. For example, the fluoroalkane difluoroethane (HFC-152a) and the fluoroalkene 1,1,1-trifluoropropene (HFO-1243zf) are each flammable and therefore not viable for use in many applications.
Higher fluoroalkenes, that is fluorine-substituted alkenes having at least five carbon atoms, have been suggested for use as refrigerants. Smutry, U.S. Pat. No. 4,788,352 is directed to production of fluorinated C5 to C8 compounds having at least some degree of unsaturation. The Smutny patent identifies such higher olefins as being known to have utility as refrigerants, pesticides, dielectric fluids, heat transfer fluids, solvents, and intermediates in various chemical reactions.
While the fluorinated olefins described in Smutny may have some level of effectiveness in heat transfer applications, it is believed that such compounds may also have certain disadvantages. For example, some of these compounds may tend to attack substrates, particularly general-purpose plastics such as acrylic resins and ABS resins. Furthermore, the higher olefinic compounds described in Smutny may also be undesirable in certain applications because of the potential level of toxicity of such compounds which may arise as a result of pesticide activity noted in Smutny. Also, such compounds may have a boiling point which is too high to make them useful as a refrigerant in certain applications.
Applicant have thus come to appreciate a need for compositions, and particularly fluid transfer compositions that are potentially useful in numerous applications, including vapor compression heating and cooling systems and methods, while avoiding one or more of the disadvantages noted above. Moreover, applicant has also recognized that in many applications there remains a need for fluorocarbon and hydrofluorocarbon-based refrigeration liquids that are environmentally safer than HFC's, possess similar or better characteristics with respect to at least certain refrigerant thermodynamic performance properties, and are compatible with existing lubricant systems.